There is known a radiation imaging apparatus that uses, as an imaging apparatus used for medical imaging diagnosis or non-destructive inspection by radiation, a flat panel detector (to be referred to as FPD hereinafter) formed from a semiconductor material. Such a radiation imaging apparatus can be used, for example, in medical imaging diagnosis, as a digital imaging apparatus for obtaining a still image or a moving image.
An integral sensor and a photon counting sensor are available as a radiation detection method used for FPDs. An integral sensor measures the total amount of charges generated from incident radiation. Meanwhile, a photon counting sensor identifies the energy (wavelength) of incident radiation and obtains the detection count of radiation for each energy level. That is, since the photon counting sensor has an energy resolution, the diagnosis capability can be improved compared to the integral sensor.
Japanese Patent Laid-Open No. 2013-501226 proposes a direct type photo counting sensor that directly detects radiation in each pixel by using CdTe. In addition, Japanese Patent Laid-Open No. 2001-194460 proposes an indirect type photo counting sensor that converts incident radiation into light by a scintillator and detects the light converted from the radiation in each pixel.